Neolitsea cassia and Cinnamomum cassia

Sorry this is not a general gardening question, but rather on identity of two distinct taxa. Perhaps taxonomists on this forum can help.

Cinnamomum cassia (L.) J. Presl (Chinese cinnamom, Chinese cassia) and Neolitsea cassia (L.) Kosterm (Grey bollywood, smooth-barb bollygum) are supposed to be two distinct plants, but both supposed to be based on same basionym Laurus cassia L.

I have a similar situation here regarding different genera. I photographed Hymenanthera crassifolia at the Botanical Gardens in Shoreline,WA around 3 weeks ago. When I came home and googled around some authorities listed it as an accepted genus Hymenanthera crassifolia while some other authorities treated it as a synonym of Melicytus crassifolius.

I still unable to determine which is the currently accepted one and which is the synonym.